(1) Field of the Invention
The present invention relates to a plastic cladding composition for a silica or glass core optical fiber, and further, to a silica or glass core optical fiber prepared from this cladding composition.
(2) Description of the Related Art
A quartz glass core optical fiber has been used in the field of long-distance communication, and means for utilizing this quartz glass core optical fiber in other fields, for example, the field of short-to-medium distance communication, is now being examined.
The quartz glass core has an excellent heat resistance over a plastic core. However, the quartz glass core optical fiber has a problem in that it is difficult to impart light transmitting characteristics to the quartz glass core optical fiber and the product is therefore expensive, and since the toughness is low, the quartz glass core optical fiber is readily broken. Means for improving the toughness of the quartz glass core optical fiber has been examined. For example, Japanese Unexamined Patent Publication No. 58-223638 proposes a quartz fiber having a protecting layer formed of a radiation-curable coating composition. This method for preparing a quartz glass core optical fiber is simpler than the heretofore developed methods, and the obtained optical fiber has an improved toughness. However, since the quartz glass optical fiber exerting a function of showing the light transmission capacity is formed by the conventional process, the product is very expensive. Accordingly, development of a method for preparing at a low manufacturing cost a quartz glass optical fiber usable as an optical fiber for medium-distance communication or short-distance communication is eagerly desired.
U.S. Pat. No. 4,511,209 discloses a cladding composition for plastic clad silica core optical fibers, which comprises a highly fluorinated monofunctional acrylate, a polyfunctional acrylate being trifunctional or higher serving as a crosslinking agent, a monofunctional or trifunctional thiol functioning as a synergist, and a photoinitiator. In order to maintain a good pliability in the formed polymer cladding, the highly fluorinated monofunctional acrylate of the cladding composition has an alkyl radical substituted with at least 12 fluorine atoms, and a specific thiol compound such as .gamma.-mercaptopropyltrimethoxysilane is used as the synergist.
According to this known technique, a plastic clad silica core optical fiber can be prepared by simplified steps. However, the compatibility of the cladding composition with the crosslinkable polyfunctional acrylate is poor and, therefore, the plastic cladding often becomes turbid and it is difficult to obtain a plastic clad silica core optical fiber having excellent light transmission characteristics.